While it remains controversial whether Article 12(1) of Singapore’s Constitution should involve a test of formal or substantive equality, the precise content of the test of formal equality itself – the “reasonable classification test” – remains unclear. This article seeks to construct a meaningful account of the reasonable classification test, that reconciles the case-law with canonical understandings of the court’s constitutional role. Three arguments are made. First, courts must identify legislative purposes only from extrinsic materials when applying the test, to avoid circularity in its application. Second, when assessing the relation between differentiation and purpose, courts must require proof of the existence, and sometimes the sufficiency, of practical reasons that excuse imperfect differentiation. Third, applicants should only bear the burden of showing that laws or decisions imperfectly differentiate, before the burden shifts to the Government to justify them. The article concludes by explaining how the reasonable classification test so understood can apply to both legislative and executive acts, even if its application may differ in certain circumstances.